If the appeal of Amanda Foreman's Georgiana, Duchess of Devonshire was in part based on her subject's resemblance to Diana, Princess of Wales, then the success of Lisa Hilton's Athénais may well depend on a perceived analogy between Louis XIV's maîtresse en titre and our own royal mistress, Camilla Parker Bowles. Both women were married when their affairs began, they were disliked by the public and adored by their lover, and each relationship remained a secret until rumour and speculation could contain it no more.

Athénais, Marquise de Montespan was also, however, widely believed to have ensured the continuation of the king's love by sacrificing newborn babies to the devil, a crime of which Camilla has not yet been accused.

But what Hilton's portrait of Athénais reveals is how similar she was to Foreman's Georgiana and how unlike both women were to anyone else. Athénais (she named herself after the goddess Athena) was to the glorious grand siècle what Georgiana was to 18th-century England: they were the celebrities of their age, absurdly privileged, enormously rich, furious gamblers, fabulously aristocratic, beautiful, highly cultivated and beloved by the wittiest dramatists of the day (Athénais had Molière at her feet, Georgiana had Sheridan). There is treachery in their lives too: each lived for years in a ménage à trois with her best friend who then displaced her. And to cap it all, they both invented a popular hairstyle: Georgiana was famed for her 2ft-high powder-puffs, stuffed with birds and plumes, while Athénais was responsible for the craze of the hurluberlu.

Athénais belongs to the biographical sub-genre of which Georgiana was precursor. In each case, the precarious youth and marketability of the writer (Lisa Hilton is 27) is played against the worldliness and sexual attraction of the aristocrat she is writing about. What this means for the young female biographer of an aristocratic celebrity, who presumably wants her book to be seen as something more than a cynical publishing ploy, is that in order to be taken seriously at all she has to write something which is, like Ophelia Field's recent life of the first Duchess of Marlborough, simply very good indeed.

Athénais comes out of the competition as an anxious and at times a vulnerable contender; there is a great deal already written on Mme de Montespan, and Hilton has to carve out new space. She finds this in the sexual attraction between Athénais and the king, with the suggestion that their insatiable lust - for one another but also for living - might be seen as the energy behind the 17th century's most splendid achievements.

Not only did Louis XIV's passionate plans for Versailles coincide with his passionate plans for Athénais, but their relationship formed the background to his uncontested years of European supremacy. It is an attractive argument, but a military historian might query the suggestion that Louis met with success in the Flanders campaign of 1667 because his "new passion made him more daring than ever."

Hilton's writing has bursts of imaginative strength, particularly at the close, and the sheer strangeness and barbarism of court life in Versailles is vividly portrayed. But Athénais would be a larger book if it were more generous, if Hilton had extended her considerable powers of empathy beyond the figure of Athénais herself.

She tends to drain the humanity from anyone not enamoured of her heroine, and heaven defend those not graced with legendary beauty. Guilty on both counts was the Queen of France, who never lost her desire for her utterly faithless husband and is written off as "frankly too unattractive for sex with her to be anything more than an obligation to the king".

Mme de Maintenon, who trumped Athénais first by stealing the king and then by marrying him, gets her due deserts here, being mocked for her lack of sexual appetite and referred to variously as "the quondam widow Scarron", "this chilly widow of 40", and that "middleaged lady". No doubt these hapless women will soon find new biographers of their own, and rise in revenge like the phoenix from ashes.

· Frances Wilson is writing a biography of the regency courtesan Harriette Wilson